Little attention has been paid in the nursing literature to practices that have tarnished the historical reputation of mental health care. This article looks at primary and secondary sources to explore the theory and implementation of an approach to treatment that became known as ‘the septic foci theory’ in the early part of the 20th century, and the careers of its two principal proponents, Henry Cotton and Thomas Graves. These medical practitioners initiated an unsubstantiated programme of surgical interventions that resulted in immeasurable pain, disfiguration and untimely deaths of countless people with mental ill health. In the institutional climate that existed at the time, doctors were able to pursue their pet theories while managers and colleagues turned a blind eye or were indifferent to what was being done. This account of the septic foci theory may prompt reflection on the importance of today's practitioners demanding evidence before implementing new treatments and the need to challenge unsafe practices on behalf of those who may not be able to mount their own challenge.